This invention relates to a device for chucking a tool or a workpiece having a cylindrical chucking surface, for example to a machine tool for driving the tool or workpiece. Conventional chucking devices for such a tool comprise a chuck with a cone-shaped aperture, in the axial direction of which a clamp ring can be screwed on the chuck. The tool, together with a cone-shaped insert member, in the central hole of which the cylindrical tool shank is received, are inserted into the cone-shaped aperture of the chuck and by means of the clamp ring, a portion of which engages the insert end, are pressed into said aperture. Due to the co-operation of the conical surfaces and the insert being slit, the insert clamps about the shank and at the same time the friction between the conical surfaces locks the insert with the tool against rotation relative to the chuck.
The tolerances for the dimensions between the conical surfaces of the chuck and insert as well as between the cylindrical surfaces of the insert and chuck must be small for bringing about the desired chucking force and precision. The tightening torque in the clamp ring yet must be high for causing the conical and cylindrical surfaces to contact each other with sufficient force.
In order to avoid to some extent the requirement of double tolerances, the tool shank can be formed conically so as to fit directly in the cone-shaped aperture of a chuck. This, however, in its turn implies higher tool costs compared with a tool having a cylindrical shank. It is also known within a certain technique to clamp, for example a tool with cylindrical shank, directly in a chuck, where the clamping force is brought about by hydraulic pressure, which acts in a hollow space in the chuck and elastically expands the aperture sides of the chuck, thereby clamping the cylindrical tool shank inserted into the aperture. By using two co-operating cylindrical surfaces for chucking, very high requirements for the dimension tolerances of the chuck and tool must be met for obtaining the desired clamping force and precision for the tool.
As appears from the aforesaid, the known chucking devices have high tolerance requirements, this implies that damage on the surfaces in question cannot be accepted and, respectively, detrimentally affects the precision and chucking of the tool.